Anti-reflective coating on oxide particles for sunscreen applications

ABSTRACT

Zinc oxide compositions and methods for applying anti-reflective coating on oxide particles for sunscreen applications are provided herein. A method includes selecting one or more coating materials to be applied to zinc oxide particles in a sunscreen composition, wherein said selecting is based on optical properties of the coating materials, wherein the optical properties comprises at least the refractive index of each of the coating materials, and applying the selected coating materials to the zinc oxide particles to create the sunscreen composition.

FIELD

The present application generally relates to chemical technology, and,more particularly, to sunscreen technologies.

BACKGROUND

Sunscreen creams and other such compositions are commonly used toprevent ultraviolet (UV) radiation (also referred to herein as “light”in this context) from reaching the skin of a human user and causingdamage. It is noted that UV light is an electromagnetic radiation with awavelength range between approximately 280 nanometers (nm) andapproximately 400 nanometers (specifically, that is the range of UVradiation that is not absorbed by the ozone).

A common active ingredient of existing sunscreen compositions is zincoxide (ZnO). ZnO is a semiconductor that has a specific band gap, andparticles of ZnO used in existing sunscreen compositions are typicallyapproximately 50-200 nm in size. Additionally, in existing sunscreencompositions, typical ZnO materials are capable of absorbing UV light(that is, blocking the UV light from passing through the sunscreencomposition to be absorbed by the skin of the user) within a wavelengthrange of approximately 290 nm through only approximately 350-380 nm.

Additionally, high sun protection factor (SPF) sunscreen compositions,which can absorb a large majority of the UV light in the range of290-380 nm, require the addition of a higher density of ZnO particles,which causes the composition to become white and/or opaque due to lightscattering from the ZnO particles, and which is an often undesirableproperty to consumers.

SUMMARY

In one embodiment of the present invention, zinc oxide compositions andmethods for applying anti-reflective coating on oxide particles forsunscreen applications are provided. An exemplary method can includesteps of selecting one or more coating materials to be applied to one ormore zinc oxide particles in a sunscreen composition, wherein saidselecting is based on one or more optical properties of each of thecoating materials, wherein the one or more optical properties comprisesat least the refractive index of each of the coating materials, andapplying the one or more selected coating materials to the one or morezinc oxide particles to create the sunscreen composition.

In another embodiment of the invention, a composition can includemultiple zinc oxide particles suspended within a medium formingsunscreen composition, and one or more coating materials applied to eachof the multiple zinc oxide particles, wherein each of the coatingmaterials has a refractive index that is between the refractive index ofair and the refractive index of zinc oxide, and wherein at least one ofthe coating materials incorporates a textured surface.

These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof illustrative embodiments thereof, which is to be read in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating coating of a ZnO particle, according toan exemplary embodiment of the invention;

FIG. 2 is a diagram illustrating a multi-layer coating of a ZnOparticle, according to an exemplary embodiment of the invention;

FIG. 3 is a diagram illustrating a roughened surface coating of a ZnOparticle, according to an exemplary embodiment of the invention; and

FIG. 4 is a flow diagram illustrating techniques, according to anembodiment of the invention.

DETAILED DESCRIPTION

As described herein, an embodiment of the present invention includeszinc oxide compositions, methods of fabrications thereof and methods ofuse thereof. Specifically, at least one embodiment of the inventionincludes one or more anti-reflective coatings (ARC) on oxide particlesfor sunscreen applications.

As further detailed herein, one or more embodiments of the inventioninclude generating ZnO compositions and methods of use thereof foreffectively blocking more and/or all of the complete spectrum of UVlight (that is, as noted above, the UV radiation that is not absorbed bythe ozone, and which ranges between approximately 280 nm and 400 nm)while also preventing whitening effects caused by the scattering oflight in the visible spectrum (that is, radiation between approximately400 nm and 700 nm). As used herein, “scattering” refers to thedeflection of rays of visible light from their original path due tointeraction with particle surfaces.

As noted above, at least one embodiment of the invention includesapplying an ARC to the outside of ZnO particles (within a sunscreencomposition) to create a core-shell structure. FIG. 1 is a diagramillustrating coating of a ZnO particle, according to an exemplaryembodiment of the invention. By way of illustration, FIG. 1 depicts asingle-layer ARC 104 applied to the outside of the ZnO particle 102. Insuch an example embodiment, the ARC 104 can be a material having arefractive index that is between that of air and ZnO, which allows lightto better couple into the ZnO particle 102 and prevents scattering atthe ZnO/air interface. In one or more embodiments of the invention,examples of ARC materials can include silicon dioxide (SiO₂), magnesiumfluoride (MgF₂), one or more fluoropolymers, aluminum oxide (Al₂O₃),zinc sulfide (ZnS), titanium dioxide (TiO₂), or one of more combinationsthereof. The selection of the particular composition of ARC material(s)can depend, for example, on the specific properties desired (by a user)from the coating.

Additionally, and as further detailed herein, in at least one embodimentof the invention, the coating(s) applied to a ZnO particle can be denseor porous. As used herein, a “dense” coating refers to a coating that issolid and contains no voids, whereas a “porous” coating refers to acoating that contains voids which may become filled with air. Further,in at least one embodiment of the invention, the coating(s) applied to aZnO particle can include surface texturing or can lack surfacetexturing.

A coating, such as utilized in one or more embodiments of the invention,can increase the light that can enter a ZnO particle, thereby increasingthe UV absorption of the particle assembly. For example, at least oneembodiment of the invention includes applying one or more ARC materialsto a ZnO particle to implement and/or manipulate a refractive indexgrading to manage the ZnO particle's interaction with light (via, forexample, absorption and scattering).

As also described herein, an optical ARC which surrounds a ZnO (or, inone or more embodiments of the invention, TiO₂) particle present in asunscreen composition reduces the scattering of light from the particlesurface. The reduction of scattering can reduce the whitening of thesunscreen for a given level of UV protection. In at least one embodimentof the invention, implementing a coating that suppresses the scatteringof visible light by the (ZnO) particles can consequently allow more ofthe UV light to be transmitted through the sunscreen layer, as opposedto being deflecting at the (ZnO) particle surface. By transmitting thevisible light instead of scattering it, the (ZnO) particles will have adecreased whitening effect (which would likely be a desirable productcharacteristic).

In one or more embodiments of the invention, such as depicted in FIG. 1,the coating can include a single layer. Additionally, and as depicted inFIG. 2, at least one embodiment of the invention can include applyingmultiple layers of coating, wherein the refractive index of the layerscan be graded between that of the ZnO and that of the ambientenvironment (for example, air).

Accordingly, FIG. 2 is a diagram illustrating a multi-layer coating of aZnO particle 102, according to an exemplary embodiment of the invention.By way of illustration, FIG. 2 depicts a coating that utilizes multiplelayers in an ARC stack, namely layer 202 and layer 104. In such anembodiment of the invention, the multiple layers (202 and 104) in theARC stack can vary in refractive index from between that of ZnO and thatof an ambient environment (for example, air) in gradations.Additionally, in one or more embodiments of the invention, a coating caninclude two or more materials that are combined in a given layer toachieve a specific refractive index.

FIG. 3 is a diagram illustrating a roughened surface coating of a ZnOparticle 102, according to an exemplary embodiment of the invention. Byway of illustration, FIG. 3 depicts a coating 104 which incorporates atextured surface 302 to enhance light in-coupling into the ZnO particle102. Roughening the surface of a coating can, by way of example,facilitate the transition from air to the ZnO particle (that is, n=2).In other words, in one or more embodiments of the invention, a roughenedsurface can be designed and implemented to perform similarly to acoating with an infinitely graded refractive index. Additionally, one ormore embodiments of the invention can include incorporating a roughenedand/or textured surface on a coating layer with or withoutadding/applying a second coating layer.

FIG. 4 is a flow diagram illustrating techniques, according to anembodiment of the present invention. Step 402 includes selecting one ormore coating materials to be applied to one or more zinc oxide particlesin a sunscreen composition, wherein said selecting is based on one ormore optical properties of each of the coating materials, wherein theone or more optical properties comprises at least the refractive indexof each of the coating materials. The refractive index of each of theone or more selected coating materials has a refractive index that isbetween the refractive index of air and the refractive index of zincoxide. Additionally, the optical properties can include reduction ofscattering at an interface of air and the one or more zinc oxideparticles.

As described herein, in one or more embodiments of the invention, theone or more coating materials can include silicon dioxide, magnesiumfluoride, one or more fluoropolymers, zinc sulfide, aluminum oxide,titanium dioxide, or one or more combination thereof. Also, the one ormore coating materials can include two or more coating materials,wherein the two or more coating materials vary in refractive index. Inone or more embodiments of the invention, the two or more coatingmaterials can be applied to the one or more zinc oxide particles indistinct layers via a gradation based on refractive index. Further, inat least one embodiment of the invention, the two or more coatingmaterials can be combined to form a single combined coating materialhaving a target refractive index.

Step 404 includes applying the one or more selected coating materials tothe one or more zinc oxide particles to create the sunscreencomposition. The techniques depicted in FIG. 4 can also includetexturing the surface of the one or more coating materials.Additionally, at least one embodiment of the invention can also includeapplying an additional one or more coating materials to the texturedsurface of the one or more coating materials.

Also, an additional embodiment of the invention includes a compositionthat includes multiple zinc oxide particles suspended within a mediumforming sunscreen composition, and one or more coating materials appliedto each of the multiple zinc oxide particles, wherein each of thecoating materials has a refractive index that is between the refractiveindex of air and the refractive index of zinc oxide, and wherein atleast one of the coating materials incorporates a textured surface. Insuch a composition, the one or more coating materials can include atleast one of (i) silicon dioxide, (ii) magnesium fluoride, (iii) one ormore fluoropolymers, (iv) aluminum oxide, (v) zinc sulfide, (vi)titanium dioxide, and (vii) one of more combinations thereof.Additionally, in such a composition, the one or more coating materialscan incorporate a textured surface, and the one or more coatingmaterials can include two or more coating materials that vary inrefractive index.

Additionally, in one or more embodiments of the invention, the two ormore coating materials can be applied to the one or more zinc oxideparticles in distinct layers via a gradation based on refractive index.Alternatively, in one or more embodiments of the invention, the two ormore coating materials can be combined to form a single combined coatingmaterial having a target refractive index.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of anotherfeature, step, operation, element, component, and/or group thereof.

At least one embodiment of the present invention may provide abeneficial effect such as, for example, applying a coating to a ZnOparticle, whereby the coating increases the light that can enter the ZnOparticle, thereby increasing the UV absorption of the particle assembly.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method, comprising: selecting one or morecoating materials to be applied to one or more zinc oxide particles in asunscreen composition, wherein said selecting is based on one or moreoptical properties of each of the coating materials, wherein the one ormore optical properties comprises at least the refractive index of eachof the coating materials; and applying the one or more selected coatingmaterials to the one or more zinc oxide particles to create thesunscreen composition.
 2. The method of claim 1, wherein the refractiveindex of each of the one or more selected coating materials has arefractive index that is between the refractive index of air and therefractive index of zinc oxide.
 3. The method of claim 1, wherein theone or more optical properties comprises reduction of scattering at aninterface of air and the one or more zinc oxide particles.
 4. The methodof claim 1, wherein the one or more coating materials comprise silicondioxide.
 5. The method of claim 1, wherein the one or more coatingmaterials comprise magnesium fluoride.
 6. The method of claim 1, whereinthe one or more coating materials comprise one or more fluoropolymers.7. The method of claim 1, wherein the one or more coating materialscomprise zinc sulfide.
 8. The method of claim 1, wherein the one or morecoating materials comprise aluminum oxide.
 9. The method of claim 1,wherein the one or more coating materials comprise titanium dioxide. 10.The method of claim 1, comprising: texturing the surface of the one ormore coating materials.
 11. The method of claim 10, comprising: applyingan additional one or more coating materials to the textured surface ofthe one or more coating materials.